The present invention concerns an arrangement for automatically controlling the level of fluidizable material in a closed channel or container for transporting and/or distributing such fluidizable material. The present invention comprises an air or gas permeable wall arranged in the channel or container and forming a partition between an upper run or pathway for the fluidizable material and a lower flue which is fed gas from a gas source via a tube, an inlet arranged in the channel or container for feeding fluidizable material to the channel or container, one or a plurality of outlets for continuous or intermittent withdrawal of material from the channel or container, and a tube for ventilating the channel or container.
The invention is particularly applicable as a "temporary" storage and distribution container for equipment used in aluminum electrolysis cells for transporting and intermittently feeding aluminum oxide and aluminum fluoride to such cells. The invention is also particularly applicable to an apportioning apparatus for sacks and bags where fluidizable material is fed in doses. The invention may, however, also be used as a plain transport channel when transporting fluidizable material from a supply area, e.g., a silo or the like, to a feeding site.
The term "fluidizable material" as used herein denotes all solids existing in a finely divided form and having such size, shape, and cohesion that the rate of feeding air streaming in at low velocity causes loss of adhesion between the finely divided particles and a reduction of their inner forces of friction.
The prior art discloses closed equipment for transporting fluidizable material where the material is apportioned from a tank or a channel-like container and where the material in the container is held between an upper level and a lower level by the use of an automatic level control. The equipment functions such that, when the material in the container reaches the lower level, an electric signal is given from the level controller. The signal then acts upon an air valve of the fluidized channel such that the material is transported from a silo or the like via a channel to the container, which then is filled. When the material in the container reaches the upper level, the signal from the level controller is cut off and the feeding of the material is stopped. The level control instrumentation may be of mechanical, optical, ultrasound, or some other type. It is, however, a disadvantage with such equipment where an automatic level control is used that the level control or level switch may fail because of wear or clogging. The equipment therefore requires extensive maintenance and repair, and is expensive to use.
Norwegian Patent No. 160, 130 shows a closed apparatus for transporting powder from a storage site to a feeding area where a horizontal or inclined transport tube is equipped with fluidizing means in the form of a channel with an upper duct for fluidizable material separated from a lower gas flue by a permeable wall. Gas or air is continuously fed to the lower gas flue such that material in the upper duct in the channel is always in a fluidized state. An equilibrium column, also serving as an outlet for the fluidized material, balances with its filling height a pressure Pf for the fluidizing gas. This solution has no level controllers, but requires a very large consumption of air/gas since the fluidizing air always at a pressure greater than Pf must be fed to the channel in order to keep it continuously filed with fluidizable material. Energy consumption therefore is great and such solution is expensive.